A sliding member using a ceramic sintered body is being applied by use of the wear resistance thereof to mechanical seal rings used in, for example, the mechanical seal of fluid equipments. The mechanical seal is one of shaft sealing devices used in the rotating parts of various types of machines with the aim of a complete fluid sealing. The mechanical seal ring is made up of a rotary ring that slidingly contacts the rotary parts of the various types of machines and is movable in the axial direction in accordance with the wear of a sliding surface, and a stationary ring that does not move. The mechanical seal ring operates to restrict the fluid leakage at the end face substantially vertical to the relative rotating shaft.
As the mechanical seal ring, a carbon material, a cemented carbide, a silicon carbide sintered body or an alumina sintered body is used mainly. In the recent years, a (porous) silicon carbide sintered body is often used which has a high hardness and high corrosion resistance and also has a low coefficient of friction during sliding and excellent smoothness.
Patent document 1 has proposed a porous silicon carbide sintered body with uniformly dispersedly arranged independent pores having a mean pore diameter of 10 to 40 μm and having a porosity of 3% to 10%. FIG. 7 is a microphotograph showing the pores existing in the porous silicon carbide sintered body proposed by the patent document 1.
In a sliding member using the silicon carbide sintered body proposed by the patent document 1, though the wear resistance thereof has been somewhat improved, a pore forming agent, such as polystyrene, for forming pores is added into the raw material powder thereof.
However, the pore forming agent is liable to aggregate. As seen in FIG. 7, this leads to a high ratio of communicating pores in which a plurality of pores are communicated with each other so as to form a long slender shape having a large maximum diameter, resulting in a high ratio of the communicating pores with respect to the pores contributing to the improvement of sliding characteristics, and having a pore diameter of 10 μm or more. Therefore, a long-term continuous use of the sliding member has caused the problem that seal properties may rapidly deteriorate because stress concentrates during sliding at the periphery of the contour forming the communicating pores, thus being susceptible to degranulation.
Patent Document 1: Japanese Unexamined Patent Publication No. 2002-147617